The goal of this proposal is to elucidate the molecular mechanism(s) that underlie pathophysiology of proteinuric kidney diseases. Work from this laboratory recently demonstrated direct regulation of actin assembly in vitro and in podocytes by dynamin, and suggested an intricate interplay between dynamin's oligomerization cycle and actin cytoskeleton dynamics. Our findings motivate the hypothesis that signaling at the slit diaphragm alters dynamin oligomerization cycle through direct dynamin-Nck interactions, which in turn initiates actin polymerization in the membrane vicinity. In Specific Aim 1 we test whether clustering of Nck on the membrane promotes dynamin oligomerization into rings, which in turn drives actin polymerization in cultured podocytes. Using small molecules that specifically promote or inhibit dynamin oligomerization, as well as our novel actin binding domain mutants of dynamin, we test whether dynamin oligomerization cycle and actin-binding interactions are essential and/or sufficient for Nck-dependent polymerization of cortical actin cytoskeleton. In Specific Aim 2 we test whether direct interactions between dynamin and Nck alter the dynamin oligomerization cycle and dynamin-dependent actin polymerization using in-vitro assays. In Specific Aim 3, using TIR-FM we test whether direct dynamin-actin interactions are essential for clathrin mediated endocytosis.